Moisture control in heat recovery apparatus



E9 @49 IF. H. KARLSSQN ET AL MOISTURE CONTROL IN HEAT RECOVERY APPARATUS Filed June 24 1944 s 'sheets-sheet 1 COOL /7/2? /N 500i 6675 (7J/7' P. H. KARLSSQN AL EOISTURE COHTROL IN HEAT RECOVERY 3 Sheets-Sheet 2 med Jun@ 24,

P. H. KARLssoN ETAL 2,468,826

MOISTURE CONTROL IN HEAT RECOVERY APPARATUS AFiled June 24, 1944 3 Sheets-Sheet 3 f f 700F fm Y doa/ 64s our f 100 50 52 JW'F 51 |hll1 Il l .a7

- Patented Maya m49 UNITED( aataszs l MOISTURE CONTROL IN HEAT RECOVERY APPARATUS Per Hunter Karlsson, wensvmeN. Y., ma nonna \S. Cooper, River Forrest, lli., alsignors to The ,j Mr lreheater Corporation, New York, N. Y.

Application J une' 24, 1944, Serial No. 541,907

The present invention method and apparatus for increasing the heat transfer efiiciency of v,air preheat'ers or the like utilized to recover heat from -hot gases, as combustion gases from a boiler. y Where cold air and hot gases are brought into l contact with metallic heat transfer surfaces either '2 claims. (ci. 25a-o) successively as in a regenerative preheater, or

simultaneously as in a recuperative heat transfer device there is a tendency, .particularly at low boiler loads, for moisture to condense from the gases on the heat transfer surfaces .at the cold end" where cold. air .is 4admitted and cooled gas is discharged.

In a regenerative air preheater operated at temperatures below the dew point of the gases sweeping over its heat exchange surface, the 'condensed moisture if left on the surface enables solid -particles carried by the gases to smear and v adhere to the surface ultimately resulting in a `reduction of capacity; in extreme cases the pas-f sages for air and gas become completely closed; In recuperative heaters, such condensation and clogging will also result in decreased heat transfer rates.

lto maintain a higher temperature of the surface at the cold' end of the apparatus.

Notwithstanding this, none of the expedients heretofore adopted have been fully satisfactory because the limit of gas exit v temperatures at which an air preheater can operate is dependent, with conventional operating methods, on the dew point of the gases passing-over the heating surfaces in such preheater. Where fuels with high sulphur content are burnedthe furnace with which an air preheater operates the dew point of the gases is high and as a consequence the exit gas temperatures at'- which an air preheater -of either -the regenerative or recuperative typev can be operated safely is correspondingly high. Where coals containing 3%v to 5% sulphur are -burned the safe gas exit temperatures permissible :are in the neighborhood of 35,0` to 400 degrees F. From thisvit may be seen that the necessityof temperature ranges where condensation would be minimized results in an accompanying loss of heat that otherwise might be recovered from the gases of combustion and this consequently involves a lowered operating emciency. 1 I

An object of the invention is to minimize th effects of clogging of the passages of an kair preheater. o l

A second object is to enable heat recovery apparatus to be operated'at anincreased `emciency by absorbing more heat than has heretofore been possible from the gases without harmful effects.

Our invention contemplates a specially constructed air preheater and a 4unique method of operating it that permits operation with its surface actuallybelow the dew temperature of the gases passing over the same and results in fa large gain in efficiency due to increased heat re#-` covery. especially when burning fuels containingv relatively large quantities of sulfur. Our unique method deliberately permits the condensation of moisture on the heat transfer surfaces, which is contrary to all prior practica-in order that the apparatus may be operated at higher efficiency. Ourmethod nevertheless avoids the usual deleterious effects in operating at such low temperavtures because the moisture which is first permitted to condense from the gases is then removed before 11,652,025, dated December 6, 1927, it will be understood that the invention is applicable to other on line gas and air flow through its passages land illus- 'confining the. operation. :of an. 'air preheater. .to 'i355 trative operating temperatures. Figure 5- is a view similar to Figure 4-but showing an arrangement in which hot gases are utilized to absorb moisture from theheattransfer surfaces instead of air as in Figure 4. Y f f As illustrated in the drawingstheair preheater is of the Ljungstrom type having a housing Il hot air outlet 34 of the preheater.

aeea'eae within which a rotor II turns to bring regenerative material I2 in its sector-shaped compartments I3 ilrst into contact with gases entering the gas side of the heater through the duct Il for absorbing heat therefrom and then into contact with air entering through the duct I5 to preheat it, the rotor being turned as by a motor I3 driving its shaft I8 through reduction gearing I'l. The sector-shaped compartments I3 are formed as usual by radial partitions orl diaphragms and the heat recovery material I2 carried in these compartments is in the form of corrugated metallic heat transfer plates; The partitions 20 carry the usual seals 22 which bear against sector plates 23, 24 opposite the ends of the rotor and act to prevent the cross flow of gas into the air side of the `preheater and of air to the gas side. This is because the imperforate portion 26 of each plate that separates the air inlet opening 30 from the gas'inlet-opening 3I and imperforate portions 21y which separate each of these from a special opening 32 located between them are all wider than the angle subtended by a sector-shaped compartment I3 of the rotor.

It will be noted that in addition to the usual gas and air openings 30, 3|, vthe sector plates are provided with additional openings 32 located betweenthe gas and air openings vwith the result that a third passage is formed for the flow of fluid through the preheater. This additional passage located between the gas and air sides of the preheater is connected at the cold end of the latter to the outlet end of a duct 33 leading from the At the hot end of the preheater the outlet end of this passage may be connected by a duct 35 to the "gasf side of an auxiliary air preheater 36 (Fig. 4) but v in any event is discharged to some point where it will not again mix with either the furnace gases or airthat pass through the preheater.

The temperature values indicated in Figure 4 are purely illustrative but serve to show that the air preheater functions at a temperature below the dew point of the gases. This is indicated by the fact that the gas outlet temperature is 300 .degrees and the air inlet temperature is 100 devover to a point below the dew point of the gases passing through. the gas side, moisture is caused to condense on the plates I2 as they again pass through the gas side of the preheater and are again contacted by gases from which the moisture becomes disentrained. Under ordinary -conditions this would not only result in eventual clogging of the passages between the plates I2 but would introduce moisture into the air passing to the furnace, which also is undesirable.

the air passage 30 of the preheater. Thus it will be seen that although are such as tovdeliberately allow condensation of moisture on the surfaces. which is. ordinarily undesirable, this moisture is removed before'the heat transfer surfaces are returned to the air passage. At the same time because the apparatus functions iny such a temperature range that the gases passing over the preheater are cooled to below their dew point. an increased amount of heat is recovered from the gases as compared with operating conditions under which it is deemed necessary to maintain the temperatures above the dew point in order to avoid condensation on heat transfer surfaces as hasheretofore been practiced.

In Figure 5 hot gas from the inlet I I is conducted to the "cold end of passage 32 by a duct By introducingthe preheated air or hot gas for drying orv absorption of the moisture condensed on the heating surface at the cold end thereof, maximum absorption of moisture is made possible and recondensation prevented by the fact that in the passages betweenthe openings 32 the carrier airas it passes downward through the Just heated surface emerging from the gas passage strikes surface of higher and higher temperatures thus preventing recondensation of the moisture picked up from the surface to be carried power consumption in installations where a fan is required in the duct 33 or 31.

By not admixing the moisture laden air or gas from discharge duct 35 with the air stream from the preheater the arrangements shown avoid return of moisture to a boiler furnace and e'liminate progressive building up of the moisture content of the heating gases entering the preheater as occurs when either hot air or gas is recirculated for simply raising the temperature of the volume of air entering the preheater. v

It is anticipated that with the arrangements and method disclosed it will be possible to operate withv gas exit temperatures from the pre'- heater corresponding to a fuel saving of 5 to 6% above that possible with present methods' of operation especially where fuels high in sulphurv and moisture must be utilized; ltherefore this method of operation has large economicalfpos'sibilities'.

What we claim is: v

1. The method oftransferring gas to a cool gas, such as air, through the medium of surfaces heated by thelgas to impart heat to the air which comprises; initially passing hot gases in contact-with heat exchange surfaces; imparting such an amount of the absorbed heat from said surfaces to air as to lower the temperature of said surfaces to a point below the dew point of the heating gases; passing hot gases over the cooled surfaces to reheat the latter, thereby causing moisture to be deposited on said surfaces from the heating gases; and passing over said surfaces a -relatively'dryvgaseous duid heated to a temperature sufficiently high to ab- 13' sorb the moisture from said surfaces prior to the 4operating conditions heat from'a hotl ace-asse again imparting heat from said surfaces to cool air.

. 2. Ina regenerative heat exchanger having a housing providing passages therethrough for hot gases and cool air respectively. inlet and outlet ducts connected tothe ends of said passages, and means for moving heat exchange materiali successively through said passages so as to absorb heat from and thereby cool the hot gas and then impart the heat to said air; means forming a third passage in the housing so located between said gas and air passages that said heat exchange material traverses said third passage upon emerging from said gas passage and prior to entering said air passage; a conduit connected to the inlet end of said third passage; means for supplying to said conduit a relatively dry gaseous fluid at a temperatureV substantially above that of the originally hot but cooled gas upon leaving the outlet o! the passage therefor as to evaporate and carry oft any moisture condensed upon said heat exchange material from the hot gas prior to contact with the cool air; a duct connected to the outlet end oi' said third passage for discharging from the system moisture laden gaseous duid passing through said third passage; an auxiliary air preheater having its gas passage interposed in said conduit; and means connecting the outlet end of the air passage o; said auxiliary'air preheater to the inlet end of the main air preheater.

PER HILMER KARLSSON.

ROLAND S. COOPER.

REFERENCES CITED lThe following references are'of record in the ille of this patent:

UNITED STATES PATENTS 

